Supermode filtering waveguide emitters

ABSTRACT

An optical apparatus comprises a semiconductor substrate, and a supermode filtering waveguide (SFW) emitter disposed on the semiconductor substrate. The SFW emitter comprises a first optical waveguide, a spacer layer, and a second optical waveguide spaced apart from the first optical waveguide by the spacer layer. The second optical waveguide is evanescently coupled with the first optical waveguide and is configured, in conjunction with the first waveguide, to selectively propagate only a first mode of a plurality of optical modes. The SFW emitter further comprises an optically active region disposed in one of the first optical waveguide and the second optical waveguide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 16/294,634 filed Mar. 6, 2019. The aforementioned relatedpatent application is herein incorporated by reference in its entirety.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to asingle-mode waveguide emitter formed from two or more vertically stackedwaveguides, and more specifically, a waveguide emitter that filters outunwanted modes through lateral radiation.

BACKGROUND

Coherent modulation formats are of primary interest for long-haul andmetro applications, and are gaining increased attention forshorter-reach and data center interconnect (DCI) applications. However,coherent modulators in silicon are inherently high-loss due tomodulating both phase and amplitude. For upcoming 600 GB, 800 GB, and 1TB applications, the transmitter insertion loss of the coherentmodulators is estimated at 25-29 dB. Meanwhile, the required transmitteroutput power into the optical fiber is between 0 and +3 dBm.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 is a top view of a transmitter with a SCOW emitter mounted on asilicon photonic chip, according to one or more embodiments.

FIG. 2 is a wafer-level view of an exemplary assembly with a quantum dotlayer, according to one or more embodiments.

FIG. 3 is a wafer-level view of an exemplary assembly including aplurality of alignment features, according to one or more embodiments.

FIG. 4 is a cross-sectional view of a supermode filtering waveguideemitter having an optically active region disposed in a ridge, accordingto one or more embodiments.

FIGS. 5A and 5B are diagrams illustrating filtering of optical modesusing a supermode filtering waveguide emitter, according to one or moreembodiments.

FIG. 6 is a diagram illustrating propagation of an optical mode using asupermode filtering waveguide emitter, according to one or moreembodiments.

FIGS. 7-10 illustrate alternate implementations of a supermode filteringwaveguide emitter, according to one or more embodiments.

FIGS. 11 and 12 illustrate altering the confinement of an optical mode,according to one or more embodiments.

FIG. 13 is a side view of a supermode filtering waveguide emittermounted on a silicon photonic chip, according to one or moreembodiments.

FIG. 14 is a method of fabricating a SCOW emitter, according to one ormore embodiments.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

One embodiment presented in this disclosure is an optical apparatuscomprising a semiconductor substrate, and a supermode filteringwaveguide (SFW) emitter disposed on the semiconductor substrate. The SFWemitter comprises a first optical waveguide, a spacer layer, and asecond optical waveguide spaced apart from the first optical waveguideby the spacer layer. The second optical waveguide is evanescentlycoupled with the first optical waveguide and is configured, inconjunction with the first waveguide, to selectively propagate only afirst mode of a plurality of optical modes. The SFW emitter furthercomprises an optically active region disposed in one of the firstoptical waveguide and the second optical waveguide.

Another embodiment presented in this disclosure is a method offabricating a supermode filtering waveguide (SFW) emitter. The methodcomprises forming a first cladding layer over a semiconductor substrate,forming a first optical waveguide above the first cladding layer,forming a spacer layer above the first optical waveguide, and forming asecond optical waveguide above the spacer layer. The second opticalwaveguide is configured, in conjunction with the first opticalwaveguide, to selectively propagate only a first mode of a plurality ofoptical modes. The method further comprises forming an optically activeregion in one of the first optical waveguide and the second opticalwaveguide, and forming a second cladding layer over the second opticalwaveguide.

Another embodiment presented in this disclosure is an optical systemcomprising a photonic chip comprising an optical component having apredefined height relative to a first surface of the photonic chip, asemiconductor substrate having a second surface, and a supermodefiltering waveguide (SFW) emitter contacting the second surface. The SFWemitter comprises a first optical waveguide, a spacer layer, and asecond optical waveguide spaced apart from the first optical waveguideby the spacer layer. The second optical waveguide is evanescentlycoupled with the first optical waveguide and is configured, inconjunction with the first waveguide, to selectively propagate only afirst mode of a plurality of optical modes. The SFW emitter furthercomprises an optically active region disposed in one of the firstoptical waveguide and the second optical waveguide. When the secondsurface contacts the first surface, one of the first optical waveguideand the second optical waveguide is optically aligned with the opticalcomponent in at least one dimension.

EXAMPLE EMBODIMENTS

To meet the required transmitter output power mentioned above, anIntegrated Tunable Laser Assembly (ITLA) would need to achieve +25 to 30dBm output, or up to 1 Watt. Such a laser may be prohibitive from bothcost and power consumption viewpoints. Currently, tunable lasers areonly available with +18 dBm output power.

An inline amplifier (e.g., micro erbium-doped fiber amplifier (EDFA))can be used to relax the required input power from the laser. However,adding the inline amplifier introduces excess noise into the modulatedsignal, which can significantly reduce transmission distance. Asmodulation format complexity increases, higher output opticalsignal-to-noise ratio (OSNR) is desired. For 1 TB optical links, greaterthan 45 dB OSNR is desired. Thus, no more than 3-4 dB of gain isachievable due to noise introduced by the inline amplifier.

Several additional challenges are encountered with integrating lasersources and other optically active components with a semiconductor-basedphotonic chip. For example, an efficient coupling of light between thelaser source and the photonic chip can require a complex and costlyoptical alignment process. To support higher data rates (e.g., throughfaster modulation and/or more optical channels), the laser source may bescaled to higher power levels. In some cases, additional opticalcomponents such as lenses and isolators may be needed to protect againstoptical feedback. In some cases, it may be necessary to attach a lasersource to a submount before integrating with the photonic chip, whichincreases fabrication costs and reduces overall fabrication yields.

According to embodiments discussed herein, an optical apparatuscomprises a semiconductor substrate, and a supermode filtering waveguide(SFW) emitter disposed on the semiconductor substrate. The SFW emittercomprises a first optical waveguide, a spacer layer, and a secondoptical waveguide spaced apart from the first optical waveguide by thespacer layer. The second optical waveguide is evanescently coupled withthe first optical waveguide and is configured, in conjunction with thefirst waveguide, to selectively propagate only a first mode of aplurality of optical modes. The SFW emitter further comprises anoptically active region disposed in one of the first optical waveguideand the second optical waveguide.

Beneficially, the optical apparatus may be more readily integrated witha semiconductor-based photonic chip. The SFW emitter provides animproved coupling efficiency due to a large mode size. Further, the SFWemitter is scalable to higher optical powers due to the large mode size,as well as low intrinsic losses and a low optical confinement factor ofthe SFW emitter. The optical apparatus enables a large optical waveguidesupporting propagation of a single optical mode. In some cases, theshape of the optical mode may be controlled through a selected materialstack-up of the SFW emitter. In some cases, the size of the optical modemay be controlled by varying a width of a ridge of the SFW emitter.

Further, the optical apparatus includes a spacer layer between the firstoptical waveguide and the second optical waveguide. The spacer layer mayoperate as an etch stop layer, which can simplify the fabricationprocess and reduce costs of producing the optical apparatus. Stillfurther, the SFW emitter may be integrated directly with a siliconsubstrate, eliminating a requirement for a separate submount. Thesilicon substrate offers additional features, such as through-siliconvias (TSVs), precise mechanical features using, e.g., photolithographyand wet etching, a high thermal conductivity, a matched coefficient ofthermal expansion (CTE) with the photonic chip. Additionally, use of thesilicon substrate enables wafer-scale processing, test, and burn-in.Although specifically discussed in terms of a silicon substrate, otherimplementations are also possible. For example, the SFW emitter may begrown on an indium phosphide (InP) substrate, and then soldered to analuminum nitride carrier and packaged in a hermetically sealed “goldbox”.

FIG. 1 is a top view of a transmitter 100 with a SFW emitter 125 mountedon a silicon photonic chip 110, according to one embodiment describedherein. The transmitter 100 includes a laser 105 aligned to an inputoptical interface 115 of the silicon photonic chip 110. In oneembodiment, the laser 105 is an integrable tunable laser assembly (ITLA)that outputs a continuous wave (CW) optical signal, but other types ofoptical sources are also contemplated. That is, the laser 105 outputs anunmodulated optical signal. However, in some cases the output power ofthe laser 105 is insufficient for performing coherent modulation.

A first waveguide 160A (e.g., a sub-micron waveguide) in the siliconphotonic chip 110 routes the CW optical signal to a spot size converter120A. Because the mode of the CW optical signal in the first waveguide160A may be much smaller than the mode size of the waveguide in the SFWemitter 125, as the CW optical signal propagates through the spot sizeconverter 120A, the spot size converter 120A increases the size of theoptical mode to better match the mode of the waveguide formed by the SFWemitter 125. As such, the optical coupling efficiency between thesilicon photonic chip 110 and the SFW emitter 125 is improved.

In FIG. 1 , the silicon photonic chip 110 defines an etched pocket 130in which at least a portion of the SFW emitter 125 is disposed. That is,FIG. 1 provides a top view of the silicon photonic chip 110 where theetched pocket 130 is etched in a direction into the page. The etchedpocket 130, which may alternately be a pocket or recess that is formedin any suitable manner, provides a space where the waveguide portion ofthe SFW emitter 125 can be disposed to align with the first spot sizeconverter 120A at an input interface and with a second spot sizeconverter 120B at an output interface of the SFW emitter 125. The secondspot size converter 120B receives the optical signal from the SFWemitter 125 and reduces the mode size so the optical signal bettermatches the mode size of a second waveguide 160B that is opticallycoupled with the second spot size converter 120B. Although the spot sizeconverters 120A, 120B are shown as being physically coupled to the firstand second waveguides 160A, 160B respectively, one or both of the spotsize converters 120A, 120B may be evanescently coupled to the first andsecond waveguides 160A, 160B.

The amplified CW optical signal generated by the SFW emitter 125 isprovided via the second waveguide 160B to a coherent modulator 135 thatperforms coherent modulation. The coherent modulator 135 modulates thedata and outputs a high-bandwidth signal capable of supporting 600 G,800 G, and 1 TB applications, and so forth. Although the embodimentsherein describe using a SFW emitter 125 to amplify a CW optical signalfor performing coherent modulation, the embodiments are not limited tosuch. For example, the SFW emitter 125 can be used to amplify CW opticalsignals before those signals are transmitted to other types ofmodulation formats that transmit data at lower speeds. Doing so maypermit the use of lower-power lasers 105 which can reduce fabricationcosts.

Although the embodiments herein describe using the SFW emitter 125 in atransmitter 100, the spot size converters 120A, 120B and the SFW emitter125 may be used in other silicon photonic applications such as a laser,a pre-amplifier, a booster amplifier, or an amplifier inside of a lossyphotonic integrated circuit (PIC) such as a high port count switch. Inthese examples, the output of the SFW emitter 125 may be coupled to adifferent optical component than the coherent modulator 135.

The modulated optical signals generated by the coherent modulator 135are output onto a third waveguide 160C that is optically coupled with anoptical fiber 150 at an output optical interface 140 of the siliconphotonic chip 110. Although not shown, the silicon photonic chip 110 mayalso include spot size converters (e.g., similar to the spot sizeconverters 120A, 1208) at the input optical interface 115 and/or theoutput optical interface 140 since the mode size of the optical signalgenerated by the laser 105 and the mode size of the waveguide of theoptical fiber 150 may be significantly different from the mode size ofthe waveguides 160A, 1608, 160C in the photonic chip 110. In anotherembodiment, the transmitter 100 may include lenses at the input opticalinterface 115 and/or the output optical interface 140 to compensate forthe different mode sizes.

FIG. 2 is a wafer-level view of an exemplary assembly 200 with a quantumdot layer 235, according to one or more embodiments. The assembly 200may be used in conjunction with other embodiments, such as used tofabricate the SFW emitter 125 of FIG. 1 . As shown in cross-sectionaldetail 205, the assembly 200 comprises a semiconductor wafer 210, a baselayer 215 disposed over the semiconductor wafer 210, a first claddinglayer 220A disposed over the base layer 215, a waveguide layer 225disposed over the first cladding layer 220A, a second cladding layer220B disposed over the waveguide layer 225, and a contact layer 240disposed over the second cladding layer 220B. Although not shown, insome embodiments, the assembly 200 may include one or more additionalwaveguide layers and/or one or more spacer layers between the firstcladding layer 220A and the waveguide layer 225.

The waveguide layer 225 comprises a first waveguide stratum 230Adisposed over the first cladding layer 220A, a quantum dot layer 235disposed over the first waveguide stratum 230A, and a second waveguidestratum 230B disposed over the quantum dot layer 235. The semiconductorwafer 210 and various layers are not drawn to scale in thecross-sectional detail. Instead, the person of ordinary skill willunderstand that the absolute and/or relative dimensioning of thesemiconductor wafer 210 and various layers may be selected to meet theneeds of individual applications.

The semiconductor wafer 210 comprises a semiconductor substrate fromwhich various optical and electrical components may be grown, patterned,etched, deposited, or eutectically bonded. In some embodiments, thesemiconductor wafer 210 comprises a bulk silicon (Si) substrate in whichone or more features or materials for the active optical device to beproduced (e.g., a laser, detector, modulator, absorber) arepre-processed. In various embodiments, the diameter of the semiconductorwafer 210 may range between about 50 millimeters (mm) and about 200 mm,and the thickness may range between about 0.3 mm and about 1 mm.However, the dimensions of the semiconductor wafer 210 may be changed toaccount for new diameters and thicknesses desired in Si (or othersemiconductor material) fabrication industries.

In some embodiments, the base layer 215 comprises a thin film of a III-Vsemiconductor material that is bonded with the semiconductor wafer 210.The base layer 215 comprises a predetermined thickness of the selectedIII-V semiconductor material, for example, between about 10 nanometers(nm) and about 1000 nm thick.

In some embodiments, the base layer 215 is formed by bonding a sheet ofthe III-V semiconductor material to the semiconductor wafer 210, whetherdirectly or indirectly (i.e., via one or more intermediate layers). Insome embodiments, a diameter of the sheet is based on the diameter ofthe semiconductor wafer 210 (e.g., within +/−5% of the wafer diameter),and a thickness of the sheet may vary independently of the thickness ofthe semiconductor wafer 210 (i.e., thicker, thinner, or the samethickness as the semiconductor wafer 210). In other embodiments, thediameter of the sheet is independent from the diameter of thesemiconductor wafer 210. For example, several small sheets may be bondedwith the semiconductor wafer 210 having a much larger diameter (e.g.,several 50 mm sheets bonded with a 300 mm semiconductor wafer 210).Various methods of bonding the sheet(s) with the semiconductor wafer 210may be used, which will be familiar to those of ordinary skill in theart. The method of bonding the sheet(s) may differ based on theparticular III-V semiconductor material of the sheet(s), and whether anyintermediate layers are used. Some non-limiting examples of the III-Vsemiconductor material of the sheet include a material selected from theboron group (i.e., a group III material: boron, aluminum, gallium,indium, thallium) and a material selected from the nitrogen group (i.e.,a group V material: nitrogen, phosphorus, arsenic, antimony, bismuth),such as, for example: boron nitride (BN), gallium nitride (GaN), galliumarsenide (GaAs), and indium phosphide (InP).

In some embodiments, an intermediate layer (not shown) may be sized witha diameter that substantially matches (e.g., +/−1%) the diameter of thesemiconductor wafer 210. In some embodiments, the thickness of theintermediate layer is in a range between about 1 nm and about 1000 nm.Some non-limiting examples of materials used in the intermediate layerinclude dielectrics such as silicon oxide (e.g., SiO₂), a polymer, ametal, and a semiconductor. Those of ordinary skill in the art will befamiliar with suitable materials that may be used as an intermediatelayer.

Further, any of the III-V semiconductor material of the base layer 215,the material of the intermediate layer, and the material of thesemiconductor wafer 210 may be doped with various other materials toprovide desired physical and/or electrical properties. For example,dopants such as silicon, carbon, zinc, germanium, tin, cadmium, sulfur,selenium, tellurium, beryllium, and/or magnesium may be used to dope theIII-V semiconductor material of the base layer 215 for use as anelectron emitter or electron collector when used in a semiconductorcomponent. Further, the sheet may be doped prior to, or after, bondingwith the semiconductor wafer 210. In another non-limiting example, boronand/or phosphorous may be used as dopants in the semiconductor wafer210.

In some embodiments, excess material is removed from the sheet afterbonding to the semiconductor wafer 210, which provides a desiredthickness to the base layer 215. For example, the excess material may beremoved from the semiconductor wafer 210 using chemical means,mechanical means, or a combination thereof.

In some embodiments, the first cladding layer 220A and the secondcladding layer 220B (which may also be referred to as matrix layers),comprises a lattice-matched material to the III-V semiconductor materialof the base layer 215. For example, aluminum gallium arsenide (AlGaAs)may be used for the first cladding layer 220A when GaAs is used for thebase layer 215. Other non-limiting examples of lattice-matched materialsinclude indium gallium phosphide (InGaP) with GaAs, and aluminum galliumindium arsenide (AlGalnAs), aluminum indium arsenide (AlInAs), indiumgallium arsenide (InGaAs), gallium arsenide antimony (GaAsSb), andindium gallium arsenide phosphide (InGaAsP) with InP. One of ordinaryskill in the art will be able to select a lattice-matched material foruse with the selected III-V semiconductor material of the base layer215.

In some embodiments, the first cladding layer 220A and the secondcladding layer 220B are epitaxially grown around the waveguide layer 225and the quantum dot layer 235. In other embodiments, the first claddinglayer 220A and the second cladding layer 220B are separately formed,e.g., the first cladding layer 220A is grown from the base layer 215 andthe second cladding layer 220B is grown from the second waveguidestratum 230B.

The first waveguide stratum 230A and the second waveguide stratum 230Bof the waveguide layer 225 comprise a III-V semiconductor material thatis grown to surround the quantum dot layer 235, and which provides astructured gain medium in which the light produced in the quantum dotlayer 235 is amplified and is directed outward from the quantum dotlayer 235 in one or more directions. In several embodiments, the III-Vsemiconductor material that comprises the first waveguide stratum 230Aand the second waveguide stratum 230B is the same as the III-Vsemiconductor material of the base layer 215, but may also be made ofdifferent III-V semiconductor materials (e.g., AlGaAs when GaAs used forthe base layer 215) and/or may be doped differently than the base layer215. In some embodiments, the first waveguide stratum 230A and thesecond waveguide stratum 230B are epitaxially grown around the quantumdot layer 235. In other embodiments, the first waveguide stratum 230A isgrown from the first cladding layer 220A, and the second waveguidestratum 230B is grown from the quantum dot layer 235.

The quantum dot layer 235 includes a plurality of quantum dots that emitphotons when stimulated by an applied electrical current. Quantum dotsare nano-structures that exhibit various properties, such as lightgeneration, based on quantum mechanical effects. The quantum dots of thequantum dot layer 235 are surrounded by the first waveguide stratum 230Aand the second waveguide stratum 230B of the waveguide layer 225, andare made of materials that have narrower bandgaps than the material ofthe waveguide layer 225. Quantum dots act as zero-dimensional entitiesthat are embedded in the waveguide layer 225, which enablesthree-dimensional capture of excited electrons (i.e., preventingmovement of the electrons). In contrast, quantum wells aretwo-dimensional structures formed by a thin layer of a first materialsurrounded by a wider-bandgap material and that only allow electroniccapture in one dimension (allowing planar two-dimensional movement ofthe electrons). As will be appreciated by one of ordinary skill in theart, the material composition and dimensioning of the quantum dots willaffect the properties of the generated light.

The contact layer 240 is made from a III-V semiconductor material. Insome embodiments, the contact layer 240 is formed of the same III-Vsemiconductor material as the base layer 215, and is doped differentlythan the base layer 215 to form an opposing semiconductor material. Forexample, when the base layer 215 is p-doped, the contact layer 240 isn-doped, and vice versa. The contact layer 240 forms the most distallayer from the semiconductor wafer 210, and along with the base layer215 surrounds the quantum dot layer 235, the waveguide layer 225, thefirst cladding layer 220A, and the second cladding layer 220B. When asufficient voltage is applied across the contact layer 240 and the baselayer 215, an electrical current will flow through the quantum dot layer235 and generate light.

As will be appreciated, various additional processes may be applied toetch semiconductor wafer 210 and various layers into a desired shape orprofile, add one or more photonic elements, and/or process the quantumdot layer 235, which are discussed in greater detail elsewhere in thedisclosure. Similarly, various wafer processes may be performed to thesemiconductor wafer 210 prior to, or after, bonding and/or growing thevarious layers. For example, one or more through-silicon vias (TSV)and/or mechanical alignment features may be added to the semiconductorwafer 210, the semiconductor wafer 210 may be diced into individualcomponents, etc., which are discussed in greater detail elsewhere in thedisclosure.

FIG. 3 is a wafer-level view 300 of an exemplary assembly 200 includinga plurality of alignment features 310, according to one or moreembodiments. More specifically, the wafer-level view 300 depicts anexterior surface 305 of the assembly 200, e.g., a surface of thesemiconductor wafer 210 opposite the base layer 215. As shown, theplurality of alignment features 310 is formed at the exterior surface305. The plurality of alignment features 310 may be used for aligningthe assembly 200 during wafer-scale processing, as well as for aligningthe individual components that are subsequently formed (e.g., diced)from the assembly 200.

The plurality of alignment features 310 may have any suitable form(s) inany suitable arrangement relative to the exterior surface 305. Theplurality of alignment features 310 may include, but are not limited to:fiducial markers suitable for optical imaging systems (e.g., sets of twoto three alignment dots in known positions), mechanical stops, metalizedmarks, poka-yoke features (e.g., go/no-go features for later fabricationsteps), epoxy slots, and other identifying features such as crosshairs,Quick Response (QR) codes, and component callouts/labels.

The plurality of alignment features 310 may include one or more featuresraised from the exterior surface 305 and/or one or more featuresrecessed (e.g., etched) into the exterior surface 305. As shown, theplurality of alignment features 310 comprises a plurality ofdifferently-shaped features that are arranged into rows. However, otherembodiments may include same-shaped features and/or different regular orirregular arrangements.

FIG. 4 is a cross-sectional view of a SFW emitter 400 having anoptically active region 445 disposed in a ridge portion 410, accordingto one or more embodiments. The SFW emitter 400 may be used inconjunction with other embodiments, such as being one exemplaryimplementation of the SFW emitter 125 depicted in FIG. 1 .

In the SFW emitter 400, the ridge portion 410 extends from a baseportion 405. Generally, the base portion 405 is significantly wider(e.g., along the x-dimension) than the ridge portion 410. As shown, theridge portion 410 comprises a second optical waveguide 440 and part of asecond cladding layer 220B. The base portion 405 comprises a firstoptical waveguide 415 arranged above the first cladding layer 220A. Thefirst optical waveguide 415 is configured to extend indefinitely (or fora distance much wider than the ridge) in the lateral dimension (e.g.,along the x-dimension). The first optical waveguide 415 may have anysuitable implementation. For example, where the first cladding layer220A comprises an indium phosphide (InP) semiconductor material, thefirst optical waveguide 415 may be formed of gallium indium arsenidephosphide (GaInAsP), aluminum gallium indium arsenide (AlGalnAs), oranother suitable quaternary compound semiconductor material. In anotherexample, where the first cladding layer 220A comprises an aluminumgallium arsenide (AlGaAs) semiconductor material, the first opticalwaveguide 415 may be formed of gallium arsenide (GaAs), AlGaAs with alower proportion of aluminum, and so forth.

The first optical waveguide 415 has a total thickness (t) along they-dimension. In some embodiments, and as depicted in FIG. 4 , the firstoptical waveguide 415 comprises a single optical waveguide layerarranged above the first cladding layer 220A and having a height (h₂)along the y-dimension. In some embodiments, the height (h₂) of thesingle optical waveguide layer equals the total thickness (t) of thefirst optical waveguide 415, but this is not a requirement. For example,FIG. 7 depicts the first optical waveguide 415 with two opticalwaveguide layers separated by a spacer layer, and FIG. 10 depicts thefirst optical waveguide 415 with an alternating arrangement ofhigh-index and low-index optical waveguide layers (e.g., a dilutewaveguide).

The ridge portion 410 comprises a second optical waveguide 440 that isspaced apart from the first optical waveguide 415. The second opticalwaveguide 440 may have any suitable implementation. For example, wherethe second cladding layer 220B comprises an indium phosphide (InP)semiconductor material, the second optical waveguide 440 may be formedof gallium indium arsenide phosphide (GaInAsP), aluminum gallium indiumarsenide (AlGalnAs), or another suitable quaternary compoundsemiconductor material. In another example, where the second claddinglayer 220B comprises an aluminum gallium arsenide (AlGaAs) semiconductormaterial, the second optical waveguide 440 may be formed of galliumarsenide (GaAs), AlGaAs with a lower proportion of aluminum, and soforth. In some embodiments, the second optical waveguide 440 isimplemented with a same material as the first optical waveguide 415, butthis is not a requirement. In some embodiments, the second opticalwaveguide 440 is formed in the waveguide layer 225.

In some embodiments, and as shown in the SFW emitter 400, an opticallyactive region 445 is disposed in the second optical waveguide 440. Inalternate embodiments (e.g., as shown in FIG. 8 ), the active region 445is disposed in the first optical waveguide 415. Any suitable opticalgain material(s) may be used in the optically active region 445, such asquantum wells, quantum dots, quantum wires, etc., which may beelectrically pumped and/or optically pumped.

The first waveguide 415 and the second waveguide 440 are spaced apart bya spacer layer 420, and form an evanescently coupled waveguidearrangement. As shown, the first optical waveguide 415 and the secondoptical waveguide 440 are “vertically stacked”, although other relativearrangements are also possible. As such, the effective refractiveindices of the modes of the independent first optical waveguide 415 andthe second optical waveguide 440 should be appropriately chosen tocreate a desired supermode that is selectively propagated by the SFWemitter 400. The effective refractive indices can be varied by changinga geometry of the first optical waveguide 415 and/or the second opticalwaveguide (e.g., a width and thickness) or materials (bulk refractiveindices). The materials and thickness of the spacer layer 420 also maybe chosen to affect the supermode properties. The arrangement of thefirst waveguide 415 and the second waveguide 440 can (and generallywill) support a plurality of supermodes. However, by virtue of thedesign of the SFW emitter 400, a fundamental supermode is confined inthe ridge portion 410, and all of the other (unwanted) supermodes arefiltered out by radiating into the lateral extent of the first opticalwaveguide 415. Thus, a single mode may be selectively propagated by theSFW emitter 400.

Referring also to FIG. 2 , for those embodiments in which the secondoptical waveguide 440 is formed in the waveguide layer 225, the firstwaveguide stratum 230A represents a first region that is doped with afirst conductivity type, and the second waveguide stratum 230Brepresents a second region that is doped with a different, secondconductivity type. The active region 445 (e.g., the quantum dot layer235) is disposed between the first waveguide stratum 230A and the secondwaveguide stratum 230B. The first optical waveguide 415 may have anysuitable doping or may be undoped.

In some embodiments, the waveguide layer 225 is formed from a III-Vsemiconductor material or alloy, and has a thickness between about 1 and2 microns. In some embodiments, a width of the ridge portion 410 (w)along the x-dimension is between about 3 and 8 microns. With suchdimensioning, a diameter of the optical mode may be about 4 and 5microns, which is much larger than most semiconductor optical amplifiers(SOAs) that support single mode amplification. As the mode sizeincreases, the optical signal typically has multiple modes. However, theSFW emitter 400 can have a large mode size and still support single modeamplification because of regions 405A, 405B of the first waveguide(s)415 away from the ridge portion 410. As an optical signal propagating inthe SFW emitter 400 generates additional modes, these modes aretransmitted into, and filtered out, by the regions 405A and 405B. Inthis manner, the SFW emitter 400 supports single mode operation atlarger mode sizes supported by other SOAs. In one embodiment, the SFWemitter 400 is a multi-mode amplifier with a vertical mode size of thefundamental mode greater than 2.5 microns 1/e² diameter, which can havesignificantly higher mode gain than any other higher order modes. In oneembodiment, the SFW emitter 400 is a single-mode amplifier with a modesize of the fundamental mode greater than 2.5 microns 1/e² diameter;other modes supported by the waveguide experience a net loss because ofthe radiation loss to 405A and 405B. The relationship 1/e² is a typicalmetric for describing the size of a Gaussian beam.

A spacer layer 420 is disposed between the first optical waveguide 415and the second optical waveguide 440. The spacer layer 420 may have anysuitable implementation, such as InP or a suitable quaternary compoundsemiconductor material. Further, the spacer layer 420 may have anysuitable doping or may be undoped. The spacer layer 420 has a height (s)along the y-dimension.

The first optical waveguide 415, the second optical waveguide 440,and/or the spacer layer 420 are dimensioned and arranged such that thefirst optical waveguide 415 and the second optical waveguide 440 areevanescently coupled. Through the evanescent coupling, the combinationof the first optical waveguide 415 and the second optical waveguide 440are configured to propagate a coupled supermode representing a sum ofthe modes of the first optical waveguide 415 and the second opticalwaveguide 440.

In some embodiments, the second optical waveguide 440 is configured topropagate a plurality of optical modes (illustrated as effective indexplots 425, 430, 435), and the first optical waveguide 415 is configuredto selectively propagate a first mode of the plurality of optical modes.Described another way, a fundamental coupled mode (illustrated by theeffective index plot 425) has an effective index that is greater thanthat of the first optical waveguide 415, and higher-order coupled modes(illustrated by the effective index plots 430, 435) have effectiveindexes that are less than that of the first optical waveguide 415. Theeffective index presented by the first optical waveguide 415 isillustrated in graphs 505, 510 of FIG. 5 . In the graph 505, aneffective index 506 is greater for a fundamental coupled mode 507 in aregion 508 corresponding to the ridge portion 410 of the SFW emitter400. In the graph 510, an effective index 511 is lesser for higher-ordercoupled modes 512 in the region 508. Thus, the fundamental coupled mode(e.g., an in-phase optical mode) is confined by the first opticalwaveguide 415, while the higher-order coupled modes (e.g., out-of-phaseoptical modes) are radiated away by the first optical waveguide 415.

According to the coupled mode theory for evanescently coupledwaveguides, the coupled system of two waveguides supports two supermodes(an in-phase mode and an out-of-phase mode) whose field profiles areapproximately described by the superposition of the individual waveguidemodes. The effective indices of these modes can be described by theequations n_(eff) ⁺=n+[Δn²+K²]^(1/2) (in-phase) and n_(eff)⁻=n−[Δn²+K²]^(1/2) (out-of-phase), where n is the effective indices ofthe two waveguides averaged, Δn is the half the difference of the twowaveguides' effective indices, and K is related to the coupling strengthbetween the two waveguides. For the SFW in the region where the upperwaveguide is etched away, the mode effective index is approximatelyequal to the effective index of the lower waveguide(s) alone, which isexpressed as n_(eff) ^(|)=n+/−Δn (sign depending on how the differencebetween waveguide effective indices is taken). It is apparent thatn_(eff) ⁺>n_(eff) ^(|)>n_(eff) ⁻ for K²>0. Since in general a mode ispulled into the region with higher refractive index, it follows that thein-phase mode is confined in the ridge portion 410, whereas theout-of-phase mode is pulled into the lateral region (with upperwaveguide etched away) where it radiates away from the ridge portion 410and the optical power is lost. By this principle, the desired in-phasemode is confined to the ridge portion 410, while the unwantedout-of-phase supermode is filtered out by radiating away.

Referring also to FIG. 6 , a diagram 600 illustrates face-view of anoptical mode using the SFW emitter 400. In some embodiments, a width (w)of the ridge portion 410 is greater than 4 microns along thex-dimension, and the coupled waveguide geometry of the SFW emitter 400has a thickness (e.g., h₁+s+t) of greater than 4 microns along they-dimension. Other sizing of the SFW emitter 400 is also contemplated. Afirst optical mode portion 605 propagates through the second opticalwaveguide 440, and a second optical mode portion 610 propagates throughthe first optical waveguide 415. Thus, the SFW emitter 400 supportspropagating an optical mode that is greater than 5 microns along thex-dimension, and greater than 4 microns along the y-dimension.

Beneficially, the large size of the optical mode allows for bettercoupling efficiency and alignment tolerance, which enables passivealignment and bonding of the SFW emitter 400. The large size of theoptical mode permits generation of very high optical power levels, e.g.,100 milliwatts to 1 watt or greater, which is approximately an order ofmagnitude greater than conventional diode lasers. Further, theamplification generated by the SFW emitter 400 can compensate for thehigher losses suffered when data rates are increased. For example, theSFW emitter 400 can be used in a transmitter that has an optical signalgreater than 50 GHz and supporting data rates between 100 Gbps and 1Tbps.

The compositions and geometries of the first optical waveguide 415and/or the second optical waveguide 440 may be selected to control asize and/or shape of the optical mode. FIGS. 7-10 illustrate alternateimplementations of the SFW emitter 400. While each of the alternateimplementations is shown with a number of features different from theSFW emitter 400, any suitable combination of the features iscontemplated.

For example, in the SFW emitter 700 of FIG. 7 , the first opticalwaveguide 415 comprises a first optical waveguide layer 705 spaced apartfrom a second optical waveguide layer 715, and a second spacer layer 710arranged between the first optical waveguide layer 705 and the secondoptical waveguide layer 715. The first optical waveguide layer 705and/or the second optical waveguide layer 715 may have any suitableimplementation, such as GaInAsP, AlGalnAs, GaAs, AlGaAs with a lowerproportion of aluminum, or a suitable quaternary compound semiconductormaterial. In some embodiments, the first optical waveguide layer 705and/or the second optical waveguide layer 715 are implemented with asame semiconductor material as the first optical waveguide 415 and/orthe second optical waveguide 440, but this is not a requirement.Further, the first optical waveguide layer 705 and/or the second opticalwaveguide layer 715 may have any suitable doping, or may be undoped.

The second spacer layer 710 may have any suitable implementation, suchas InP or a suitable quaternary compound semiconductor material. In someembodiments, the second spacer layer 710 is implemented with a samesemiconductor material as the spacer layer 420, but this is not arequirement. Further, the second spacer layer 710 may have any suitabledoping or may be undoped.

A first conductive contact layer 720 is arranged above the secondcladding layer 220B (e.g., an upper cladding layer). A second conductivecontact layer 725 arranged beneath the first cladding layer 220A (e.g.,a lower cladding layer). In such a case, the second cladding layer 220Band the second waveguide stratum 230B of the waveguide layer 225 may bedoped with a first conductivity type. The first cladding layer 220A, thefirst waveguide stratum 230A of the waveguide layer 225, and/or thefirst optical waveguide layer 705 and the second optical waveguide layer715 may be doped with a different, second conductivity type. In someembodiments, the spacer layer 420 is also doped to be electricallyconductive.

In the SFW emitter 800 of FIG. 8 , the optically active region 445 isdisposed in the first optical waveguide 415 (i.e., in the base portion405). A first optical waveguide layer 805 of the first optical waveguide415 is arranged beneath the spacer layer 420 and above the opticallyactive region 445, and a second optical waveguide layer 810 of thesecond optical waveguide 415 is arranged beneath the optically activeregion 445 and above the first cladding layer 220A.

The first optical waveguide layer 805 and/or the second opticalwaveguide layer 810 may have any suitable implementation, such as suchas GaInAsP, AlGalnAs, GaAs, AlGaAs with a lower proportion of aluminum,or a suitable quaternary compound semiconductor material. In someembodiments, the first optical waveguide layer 805 and/or the secondoptical waveguide layer 810 is implemented with a same semiconductormaterial as the first optical waveguide 415 and/or the second opticalwaveguide 440, but this is not a requirement.

The first conductive contact layer 720 is arranged above the secondcladding layer 220B, and the second conductive contact layer 725arranged beneath the first cladding layer 220A. In such a case, thefirst optical waveguide layer 805, the waveguide layer 225, and thesecond cladding layer 220B may be doped with a first conductivity type,and the second optical waveguide layer 810 and the first cladding layer220A may be doped with a different, second conductivity type.

In the SFW emitter 900 of FIG. 9 , the first conductive contact layer720 is arranged above the second cladding layer 220B, and the secondconductive contact layer 905 is arranged above the spacer layer 420.Within the second conductive contact layer 905, conductive contacts910A, 910B are arranged on opposite sides of the ridge portion 410.Beneficially, as the optical field is relatively low in the conductivepaths across the spacer layer 420 to the first waveguide stratum 230A ofthe waveguide layer 225, in some cases the first optical waveguide 415may be undoped, which reduces optical losses in the first opticalwaveguide 415.

In the SFW emitter 1000 of FIG. 10 , the first optical waveguide 415comprises a dilute waveguide having an alternating arrangement of higheffective index layers 1005A, 1005B, 1005C and low effective indexlayers 1010A, 1010B. Although three (3) high effective index layers1005A, 1005B, 1005C and two (2) low effective index layers 1010A, 1010Bare shown, any alternate numbers are also contemplated. Further, thedimensioning of the high effective index layers 1005A, 1005B, 1005C andthe low effective index layers 1010A, 1010B (e.g., along they-dimension) may be controlled to provide a desired size and shape ofthe optical mode.

FIGS. 11 and 12 illustrate altering the confinement of an optical mode,according to one or more embodiments. The features illustrated indiagrams 1100, 1200 may be used in conjunction with other embodiments,such as with any of the SFW emitters 400, 700, 800, 900, 1000.

In the diagram 1100 (e.g., representing a first cross-section view ofthe SFW emitter), the ridge portion 410 and the second optical waveguide440 have a width W1 along the x-dimension. In the diagram 1200 (e.g.,representing a second cross-section view of the SFW emitter), the ridgeportion 410 and the second optical waveguide 440 have a width W2 that isless than width W1. The SFW emitter having the width W1 provides arelatively greater confinement in the second optical waveguide 440,resulting in a relatively greater optical intensity of the first opticalmode portion 605, and a relatively lesser optical intensity of the ofsecond optical mode portion 610. The SFW emitter having the width W2provides a relatively lesser confinement in the second optical waveguide440 (compared to the width W1), resulting in a relatively lesser opticalintensity of the first optical mode portion 605, and a relativelygreater optical intensity of the of second optical mode portion 610.

In this way, the second optical waveguide 440 has different widths alonga length of the ridge portion 410 (as shown, extending into and out ofthe page). Thus, by adjusting the width of the ridge portion 410 and thesecond waveguide 440, the SFW emitter may be used to provide a variableconfinement SOA, e.g., where high optical gain is required in one regionand high optical power is required in another region. Additionally, byadjusting the width of the ridge portion 410 and the second waveguide440, the SFW emitter may be used to provide an optical apparatus with alarge optical mode at an external interface and small optical mode inthe bulk of the optical apparatus.

FIG. 13 is a side view 1300 of a SFW emitter 125 mounted on a siliconphotonic chip 110, according to one or more embodiments. The featuresdepicted in the side view 1300 may be used in conjunction with otherembodiments, e.g., such as with any of the SFW emitters 400, 700, 800,900, 1000.

The silicon photonic chip 110 includes an insulator layer 1305 (e.g., aninterlayer dielectric (ILD) disposed on a silicon substrate 1310 (e.g.,a monocrystalline silicon substrate). During fabrication, the insulatorlayer 1305 is processed to form the spot size converters 120A, 120Bwhich transfer an optical signal into, and receive an amplified opticalsignal from, the SFW emitter 125 as well as the waveguides 160A, 160B(e.g., silicon nitride or silicon oxynitride waveguides).

As shown, the SFW emitter 125 is arranged within the etched pocket 130formed in the insulator layer 1305, such that respective ends of awaveguide 1320 in the SFW emitter 125 (shown generally by the dashedlines) are aligned with the spot size converters 120A, 120B. As shown,the etched pocket 130 extends fully through the insulator layer 1305 toa surface 1325 of the silicon substrate 1310. In other embodiments,however, the etched pocket 130 extends only partly through the insulatorlayer 1305. The SFW emitter 125 includes a ridge portion 410 and anoptically active region 445 (e.g., formed in a quantum dot layer) whichconfine the optical signal within the waveguide 1320 and provide opticalamplification. The functions of these components are discussed ingreater detail above.

As shown, a submount 1335 such as a silicon substrate is disposed abovethe insulator layer 1305. When aligning the SFW emitter 125 with thespot size converters 120A, 1208, an external surface 1330 of thesubmount 1335 is brought into contact with an external surface 1315(e.g., a top surface of the insulator layer 1305) of the siliconphotonic chip 110. Although not shown, an adhesive may be used to fastenthe submount 1335 to the external surface 1315 to thereby maintain thealignment between the waveguide 1320 and the spot size converters 120A,1208.

In one embodiment, the SFW emitter 125 includes at least two conductivecontacts for providing power to perform optical amplification on anoptical signal propagating through the waveguide 1320. In one example,the two conductive contacts are disposed on a top surface of thesubmount 1335 (e.g., outside the etched pocket 130) and are wire bondedor otherwise electrically coupled with a power source on the siliconphotonic chip 110 or another chip. In another example, at least oneconductive contact is disposed on the top surface of the submount 1335while another electrode is disposed on a bottom surface of the ridgeportion 410 (e.g., the side of the ridge portion 410 facing with thesurface 1325). In this case, the silicon photonic chip 110 may includean electrode on the surface 1325, which is then soldered or otherwiseelectrically coupled with the conductive contact disposed on the bottomsurface of the ridge portion 410 for providing power to the SFW emitter125.

FIG. 14 is a method 1400 of fabricating a SFW emitter, according to oneor more embodiments. The method 1400 may be used in conjunction withother embodiments, such as fabricating any of the SFW emitters 400, 700,800, 900, 1000.

The method 1400 begins at block 1405, a first cladding layer is formedover the semiconductor substrate. At block 1415, a first opticalwaveguide is formed above the first cladding layer. At block 1425, aspacer layer is formed above the first optical waveguide. At block 1435,a second optical waveguide is formed above the spacer layer. At block1445, an optically active region is formed in one of the first opticalwaveguide and the second optical waveguide. In some embodiments, block1445 is performed as part of block 1435: a lower portion of the secondoptical waveguide is formed above the spacer layer, the optically activeregion is formed above the lower portion, and an upper portion of thesecond optical waveguide is formed above the optically active region. Atblock 1455, a second cladding layer is formed above the second opticalwaveguide (e.g., above the upper portion of the second opticalwaveguide). At block 1465, a ridge extending from a slab is formed. Insome embodiments, an etching process is used to form the ridge, and thespacer layer operates as an etch stop layer. At block 1475, one or moreconductive contacts are formed. In some embodiments, the one or moreconductive contacts are formed above the second cladding layer (e.g. onthe ridge), and either (1) above the spacer layer or (2) beneath thefirst cladding layer (e.g., after separation from the semiconductorsubstrate). The method 1400 ends following completion of block 1465.

In the preceding, reference is made to embodiments presented in thisdisclosure. However, the scope of the present disclosure is not limitedto specific described embodiments. Instead, any combination of thedescribed features and elements, whether related to differentembodiments or not, is contemplated to implement and practicecontemplated embodiments. Furthermore, although embodiments disclosedherein may achieve advantages over other possible solutions or over theprior art, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the scope of the present disclosure. Thus,the preceding aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s).

Aspects of the present disclosure are described with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodimentspresented in this disclosure. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality and operation of possible implementations ofsystems, methods and computer program products according to variousembodiments. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment, or portion of code, whichcomprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block may occurout of the order noted in the figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

We claim:
 1. An optical apparatus comprising: a semiconductor substrate;and a supermode filtering waveguide (SFW) emitter disposed on thesemiconductor substrate and formed as a first portion extending from asecond portion, the SFW emitter comprising: a first optical waveguidedisposed in the second portion; a spacer layer; a second opticalwaveguide disposed in the first portion and spaced apart from the firstoptical waveguide by the spacer layer, wherein the second opticalwaveguide is evanescently coupled with the first optical waveguide andconfigured in conjunction with the first optical waveguide toselectively propagate only a first mode of a plurality of optical modes;and an optically active region disposed in one of the first opticalwaveguide and the second optical waveguide.
 2. The optical apparatus ofclaim 1, wherein the first optical waveguide comprises: a first opticalwaveguide layer spaced apart from a second optical waveguide layer; anda second spacer layer arranged between the first optical waveguide layerand the second optical waveguide layer.
 3. The optical apparatus ofclaim 1, wherein the second portion comprises a semiconductor materialbonded to the semiconductor substrate.
 4. The optical apparatus of claim1, wherein the first optical waveguide in the second portion isdimensioned to filter out one or more other modes of the plurality ofoptical modes.
 5. The optical apparatus of claim 1, wherein theoptically active region is disposed in the first portion.
 6. The opticalapparatus of claim 1, wherein the optically active region is disposed inthe second portion.
 7. The optical apparatus of claim 1, wherein thesecond optical waveguide has different widths along a length of thefirst portion, and wherein the different widths alter a confinement ofthe first mode as an optical signal propagates through the secondoptical waveguide.
 8. The optical apparatus of claim 1, furthercomprising: an upper cladding layer arranged above the spacer layer; afirst conductive contact layer arranged above the upper cladding layer;a lower cladding layer arranged beneath the first optical waveguide; anda second conductive contact layer arranged at one of: (1) above thespacer layer, and (2) beneath the lower cladding layer.
 9. The opticalapparatus of claim 1, wherein the first optical waveguide comprises analternating arrangement of high effective index layers and low effectiveindex layers.
 10. The optical apparatus of claim 1, wherein theoptically active region comprises one or more of quantum wells, quantumdots, and quantum wires.
 11. A method of fabricating a supermodefiltering waveguide (SFW) emitter, the method comprising: forming afirst cladding layer over a semiconductor substrate; forming a firstoptical waveguide above the first cladding layer; forming a spacer layerabove the first optical waveguide; forming a second optical waveguideabove the spacer layer by forming a first portion extending from asecond portion, wherein the first optical waveguide is disposed in thesecond portion, wherein the second optical waveguide is disposed in thefirst portion, and wherein the second optical waveguide is configured,in conjunction with the first optical waveguide, to selectivelypropagate only a first mode of a plurality of optical modes; forming anoptically active region in one of the first optical waveguide and thesecond optical waveguide; and forming a second cladding layer over thesecond optical waveguide.
 12. The method of claim 11, wherein the secondportion comprises a semiconductor material bonded to the semiconductorsubstrate.
 13. The method of claim 11, wherein the first opticalwaveguide in the second portion is dimensioned to filter out one or moreother mode of the plurality of optical modes.
 14. The method of claim11, wherein forming the first portion comprises: etching to the spacerlayer through at least the second cladding layer.
 15. The method ofclaim 11, wherein the second optical waveguide is formed with differentwidths along a length of the first portion, and wherein the differentwidths alter a confinement of the first mode as an optical signalpropagates through the second optical waveguide.
 16. An optical systemcomprising: a photonic chip comprising an optical component having apredefined height relative to a first surface of the photonic chip; asemiconductor substrate having a second surface; and a supermodefiltering waveguide (SFW) emitter contacting the second surface andformed as a first portion extending from a second portion, the SFWemitter comprising: a first optical waveguide disposed in the secondportion; a spacer layer; a second optical waveguide disposed in thefirst portion and spaced apart from the first optical waveguide by thespacer layer, wherein the second optical waveguide is evanescentlycoupled with the first optical waveguide and configured, in conjunctionwith the first optical waveguide, to selectively propagate only a firstmode of a plurality of optical modes; and an optically active regiondisposed in one of the first optical waveguide and the second opticalwaveguide, wherein, when the second surface contacts the first surface,one of the first optical waveguide and the second optical waveguide isoptically aligned with the optical component in at least one dimension.17. The optical system of claim 16, wherein the second portion comprisesa semiconductor material bonded to the semiconductor substrate.
 18. Theoptical system of claim 16, wherein the semiconductor substrate definesone or more mechanical features relative to the second surface, whereinthe one of the first optical waveguide and the second optical waveguideis optically aligned with the optical component when the one or moremechanical features are contacted with corresponding portions of thephotonic chip.
 19. The optical system of claim 16, wherein the firstsurface is defined by an insulator layer of the photonic chip, andwherein the optical component is formed in the insulator layer.
 20. Theoptical system of claim 19, wherein a cavity is formed in the insulatorlayer from the first surface, wherein the second surface makes contactwith the first surface on opposing sides of the cavity, and wherein theSFW emitter is disposed in the cavity.